Internal double bonds are notoriously difficult to polymerize in an insertion mode unless they are incorporated as cis bonds in strained rings. While insertion polymerization examples of 3-, 5-, and strained bicyclics (norbornene derivatives) are common, noticeably absent are examples of 4-membered rings. Although cyclobutene has sufficient ring strain, 31 kcal/mol (Schleyer, P. v. R. et al., J. Am. Chem. Soc. 1970, 92, (8), 2377), very few examples of vinylic polymerization of cyclobutene are known. This is due to the fact that simple cyclobutenes will undergo rapid pericyclic ring opening reactions to form butadiene or alternatively undergo ROMP. Attempts to polymerize cyclobutene results in a polymer that contain both the cyclobutene repeats and 1,4-butadiene repeat units. These butadiene repeats decrease the thermal stability of the polymer (Dall'asta, G. et al., Die Makromolekulare Chemie 1962, 56, (1), 224).
In 1960s, Dall'asta and his co-workers reported several publications of polymerization of cyclobutene, however their polymer contains butadiene units and ring opening polymerization units. Also, the molecular weight information is obscure (See, e.g., Dall'asta, G. Journal of Polymer Science, Part A; Polymer Chemistry 1968, 6, 2397; Natta, G. et al., G. Die Makromolekulare Chemie 1963, 69-1, 163). They also tried to polymerize a fused ring system, but the resulting polymer has quite low molecular weights and contains ring opened units up to 10 mol % (Dall'asta, G. Journal of Polymer Science, Part A: Polymer Chemistry 1968, 6, 2405). To the best of our knowledge, no reports of high molecular weight, genuine vinylic polymer of any cyclobutene derivatives have been published.
In recent years a number of new high performance engineering materials have been prepared through the insertion polymerization of norbornene. These polymers can have outstanding properties, such as low moisture absorption, low dielectric constants, chemical resistance, low birefringence, high breakdown voltages and high glass transition temperatures. A number of those polynorbornene Materials are now commercially available and include Appear® optical polymer material for flat panel display and waveguides, Aprima® adhesives and cover-coat, Avatrel® materials, Duvcor® 193 nm and 157 nm photoresists (Promerus), as well as copolymer of olefins and norbornenes, Topas® (Topas Advanced Polymers) and Apel ® (Mitsui Chemical).
As stated earlier, the insertion polymerization of the 4-membered ring, although highly strained, has been less successful. The unwanted pericyclic ring-opening of cyclobutene to the more stable butadiene has limited advancement in this field.